UNION members at Ryde metal castings company, Trucast, are being balloted on industrial action.
Doncasters, which owns the company that produces turbocharger impellers, is implementing a continental shift pattern after a 90-day consultation on the changes, which were not agreed with shopfloor workers.
A worker said: "The company is implementing the new shift pattern, reducing tea breaks and holiday payments and only offering a small shift premium that doesn’t cover the benefits lost."
In a statement, Doncasters Trucast said the changes in contracts reflected the need to align manpower with current market demand.
Late last year, in response to a protracted slump in demand and as a consequence of the uncertain global financial situation, Trucast reduced its workforce, resulting in a number of redundancies, but now the number of employees was increasing in line with demand.
Clive Thomas, managing director of Doncasters TurboChargers Division, said: "Production processes at Trucast operate most efficiently when there is continuous working — in other words, machinery is not stopped and started with a four-hour interruption between shifts.
"The changes made to the contracts reflect this, altering current shift patterns to achieve continuous production."
He said although the changes were unsettling for some employees, they would help safeguard the future of the site.
Another worker, who would not be named, said: "After the fiasco of the redundancies towards the end of last year, they are now re-employing after realising it was a big mistake.
"They are now issuing workers with new contracts, which remove benefits negotiated over the years.
"The rotating continental shift disrupts family and social life and spoils any chance of going to college or taking on part-time work to cover the shortfall.
"This has also followed a pay freeze. We could maybe understand the move if the company had made no profit last year but, reportedly, it made £9 million."